The spatial distribution of large gaged floods throughout the
United States shows that the locations of most of the largest flows
are related to specific combinations of regional climatology,
topography, and basin size. Key factors include the general northward
trend of decreasing atmospheric moisture, proximity to oceanic
moisture sources such as the Pacific Ocean and the Gulf of Mexico,
and orientation of topographic features relative to directions of
moisture flow, with the largest flows being at locations where
topographically high areas are oriented perpendicular to directions
of moisture flow. Additionally, the largest flows in large river
basins are primarily caused by persistent climatologic conditions
such as seasonal snowfall. In contrast, the largest flows in smaller
basins are most commonly the result of intense precipitation due to
convective storms.

Contents

Floods-A National Hazard
Largest of the Large
Where Are the Largest Flows?
Why Are Large Flows Where They Are?
Summary
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